1. Field of the Invention
This invention is related to a vacuum sheet feeding apparatus and more particularly to a selectively movable valve for controlling the area of vacuum application transverse to the sheet feed path of a sheet feeding apparatus, the position of the valve being dependent upon the size of the sheets being fed.
2. Description of the Prior Art
In the copier/duplicator field, it is well known to feed sheets from a stack seriatim by vacuum pick-off apparatus. While intermittently moving fingers or sucker arms have been used in the past, more recently oscillating (or rotating) vacuum cylinders have been utilized for sheet feeding in order to achieve higher operational speeds. Generally, the oscillating or rotating vacuum cylinder feed apparatus include a ported cylindrical housing in juxtaposition with a stack of sheets to be fed. A vacuum source connected to the housing creates a reduced pressure atmosphere which induces the tacking of a sheet to the surface thereof and holds it there while the rotation of the housing strips the sheet from the stack and delivers the sheet to a downstream feeding mechanism.
If a vacuum feed apparatus is required to handle sheets of varying widths (in the transverse direction to the sheet feed path), care must be taken to insure that all open ports in the housing are covered by a sheet being fed or the effectiveness of the vacuum may be lost. To accomplish this end, the ports may be located only within the marginal dimension of the narrowest sheet to be fed, or a valve may be provided to close the outboard ports when a sheet of narrower dimension is being fed. If the ports are located within the narrowest marginal dimension of a sheet to be fed, the outside marginal edges of wider sheets will now be under vacuum control during feeding and may cause jamming of the feeder. On the other hand, a valve to control outboard ports has heretofore required operator intervention during the feed cycle to assure proper setting of the valve dependent on the size of sheets being fed.